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Nikiforov, Andriy (2007): Measurements of the Neutral Current ep Cross Sections Using Longitudinally Polarised Lepton Beams at HERAII. Dissertation, LMU München: Fakultät für Physik



This thesis presents inclusive $e^\pm p$ single and double differential cross sections for neutral current deep inelastic scattering measured as functions of the four-momentum transfer squared $Q^2$ and the Bjorken variable $x$ in interactions of longitudinally polarised leptons with unpolarised protons using the H1 detector at HERA~II. An overview of the phenomenology of deep inelastic scattering is given and the experimental apparatus as well as the measurement and analysis procedures are described. The analysis is based on $e^+p$ data taken in 2003-04 and $e^-p$ data taken in 2005 at a centre-of-mass energy of $\sqrt s = 318$~GeV, with integrated luminosities of 47.6~pb$^{-1}$ and 98.4~pb$^{-1}$ for the $e^+ p$ and $e^- p$ samples, respectively. The cross sections are measured in the range of $200 < Q^2 < 20\,000$~GeV$^2$ and $0.0032<x<0.65$. The measurements are used to study polarisation effects in neutral current interactions and to determine the structure function $x\tilde{F}_3$. The new HERA~II data are combined together with previously published data from HERA~I to determine the structure function $x\tilde{F}_3$ with improved precision. Furthermore, this measurement is combined with the corresponding ZEUS measurement to provide the most accurate measurement of the interference structure function $xF_3^{\gamma Z}$, which is sensitive to the valence quark distributions down to low values of $x$. The data on polarised cross section asymmetries $A^\pm$ are also combined with the ZEUS data. This leads to the first observation of parity violation in neutral current $e^\pm p$ scattering at distances down to $10^{-18}$~m. The data are well described by the Standard Model predictions.